BRUSSELS (Reuters) - Pakistan must play a positive role in bringing stability to Afghanistan as foreign troops prepare to leave in 2014, the head of NATO said on Tuesday, before a U.S.-chaired meeting that will try to ease friction between often feuding neighbors.

U.S. Secretary of State John Kerry will host talks between Afghan President Hamid Karzai and senior Pakistan officials in Brussels on Wednesday, with the aim of calming tension over border disputes and the stalled peace process.

"If we are to ensure long-term peace and stability in Afghanistan we also need a positive engagement of Afghanistan's neighbors, including Pakistan," NATO Secretary-General Anders Fogh Rasmussen told reporters as alliance foreign ministers met in Brussels to discuss NATO's mission in Afghanistan.

Wednesday's U.S.-chaired meeting is part of a series of on-off discussions between Afghanistan and Pakistan at the behest of the United States. Rasmussen said he would meet Karzai later on Tuesday.

Afghanistan has grown increasingly frustrated with Pakistan over efforts to pursue a peace process involving the Taliban, suggesting that Islamabad is intent on keep Afghanistan unstable until after foreign combat forces have left at the end of 2014.

U.S. officials hope that Kerry, who has a good relationship with Karzai, can bring the parties back to the negotiating table and make constructive progress on an issue that has long-term security implications for Washington.

Kerry said on Monday the aim of the meeting would be to "try to talk about how we can advance this process in the simplest, most cooperative and most cogent way, so that we wind up with both Pakistan's and Afghanistan's interests being satisfied, but, most importantly, with a stable and peaceful Afghanistan."

TENSION

The talks follow weeks of tension with Pakistan over their 2,600 km (1,600 mile) border and stalled peace efforts.

Although there have been several meetings in Western capitals over the past few months in which representatives of the Taliban have met Afghan peace negotiators, there have been no signs of a breakthrough.

Kabul accuses Pakistan of harboring the Taliban leadership in the city of Quetta and using militants as proxies to counter the influence of India in Afghanistan.

As well as Karzai and Kerry, Wednesday's meeting will include Afghanistan's defense minister, Bismillah Khan Mohammadi, Pakistan's army chief, General Ashfaq Kayani, and Pakistan's foreign secretary, Jalil Jilani, the U.S. official said.

NATO-led forces are expected to cede the lead role for security in Afghanistan this spring to Afghan soldiers, 12 years after the United States invaded Afghanistan to oust the Taliban government harboring Osama bin Laden, the al Qaeda leader who masterminded the September 11, 2001 attacks on U.S. cities.

Most foreign combat forces are due to pull out by the end of 2014, leaving a smaller NATO-led training mission behind and a U.S. force to fight militants.

The White House has yet to decide how many U.S. troops will remain in Afghanistan after 2014 and this could be a factor influencing both Taliban and Pakistani strategy. Much depends on progress in negotiations with Karzai on a Bilateral Security Agreement to define the future legal status of U.S. forces.

NATO defense ministers meeting in Brussels on February 22 discussed keeping a combined NATO force of between 8,000 and 12,000 troops. That compares to combined NATO forces of about 100,000 troops in Afghanistan now.

General James Mattis, the head of the U.S. military's Central Command, said in March he had recommended keeping 13,600 American troops in Afghanistan after 2014.